You've answered your own question. Cars are dumb machines because we don't yet have the technology to judge what is "crazy fast" and make decision about where it should be allowed. Other than the obvious reasons of racing and car enthusiasts, there are legitimate reasons for a car to do 100mph. Often in emergency situations, you need to speed up rather than slow down to prevent an accident. If we start placing limits on people's cars, there will almost certainly be accidents caused by that, because the last thing you want in a situation where you need to react quickly is the car not doing what you want it to.
WRT "Cars are dumb machines" I find it fascinating in this discussion that its assumed we can trivially deploy an AI smart enough to out drive a human, but nobody wants to talk about humans being so dumb they get drunk then go driving after decades of incessant propaganda and punishment. I don't think a species that can't stop drunks from driving stands a chance at creating an AI that can outdrive humans.
Stopping drunks from driving is a political/social problem, not a technical problem. IIDs have been around for a long time, but mandating their installation on every sold car is political suicide in most places (though it seems some countries like Sweden are considering it).
